Patent GB-594074-A (GB)
Title: An improved means for controlling the operation of aircraft engines
IPC: F02D9/00
Filed: 1944-05-12
Abstract: 594,074. Fluid-pressure servomotors. GENERAL MOTORS CORPORATION. May 12, 1944, No. 9170. Convention date, July 6, 1942. [Class 135] [Also in Group XXVII] In a variable - datum boostcontrol mechanism for supercharged aircraft engines, the action of the manually-operable pressure-selection device is modified independently by the throttle valve servomotor so that with increasing altitude the intake pressure is reduced and the power output is less than that corresponding to the selected pressure. The automatic mechanism controls the throttle valve and is contained in a housing 2, Figs. 1 and 6, and that for the engine and propeller speed and for adjusting the richness of the fuel air mixture in an adjacent housing 4. Within the housing 2 a pivot 138 is mounted between an evacuated bellows 196 and a bellows 198 open to an inlet manifold pressure which is so chosen that if the bellows 196 should collapse, the device can still be operated manually. A lever 136< > on the pivot 138 is connected at one end to a servomotor control valve 80 slidable in a guide 82 and controlling a high-pressure oil flow which operates a piston 34 on a rod 32 linked to one arm 28 of a differential lever of which the other arm 14 is adjustably connected by a rod 12 to the throttle valve (not shown). The other end of the lever 136 is adjustably fixed by a, manually-operated cam 144 on a shaft 146 mounted in an eccentric sleeve 148, Fig. 11, rotated by an arm 156 linked to the end of the piston-rod 32. The shaft 146 is rotated by an arm 160, Fig. 1, and a rod 172 connected to an arm 180 fixed to a shaft 20 which is itself turned by a lever 186 comprising two resiliently connected parts 186A, 186B of which the arm 186A is connected to the pilot's control lever. Also rigidly secured to the shaft 20 is an arm 18 carrying a stud 17A about which the lever 28, 14 pivots so that when the control lever is operated the lever moves bodily with consequent adjustment of the throttle valve. To avoid excessive engine speed, a shaft driven by the engine carries a centrifugal governor adapted to close an electric switch when the speed reaches a predetermined maximum, and closure of the switch energizes a solenoid 432, Fig. 6, which displaces an armature 434, the rod 436 of which moves the valve 80 to the left causing the servomotor piston 34 to move to the right and reduce the throttle opening. When the speed falls off, a spring 438 returns the armature 434, the action being delayed by a dashpot device. The shaft 20, Fig. 7, carries a toothed sector 230 adapted to rotate a cam member 234, a cam track 238 on which guides a follower 240 on an arm 242 connected to the control mechanism for varying the pitch of the propeller. The outer surface 380 of the cam member 234 determines whether the combustible mixture supplied to the engine is lean for cruising or rich for other purposes, the surface being formed with a recess 382 into which spring 406 thrusts a valve member 404 which controls a servomotor piston 272. The piston 272, through its rod 280, rocks a lever 306 linked to an arm 320 secured to a sleeve 322, Fig. 9, having a perforated flange 350 pressed by a spring, 352 against a studded flange 346 on a sleeve 324 frictionally connected to a mixture control device 330. The connection between the flanges 350, 346 permits the control to be overridden manually by a lever 364 on an annulus 362 operatively associated with an inner sleeve 360 through a lostmotion connection which permits the automatic control to operate over as much as 30 degrees of arc before affecting the manual control lever. The sleeve 360 is secured to a plate 338 forming part of the friction drive between the sleeve 334 and the mixture control 330. In operating the device, a cam 144 is set to give the selected maximum inlet manifold pressure by securing the ends of the rod 172 in appropriate holes 170, 178 in the levers 160, 180. The lever 186 is actuated by the pilot's lever 500, Fig. 19, connected to the arm 186A and during normal operation the lever 500 is retained in its adjusted position by teeth 503 engaging a rack on a fixed sector 505. In emergency, the lever is pushed beyond the normal limits, the teeth 503 move to a plain portion 513 of the sector 505 and a spring-pressed pad 520 engages the lever making it necessary for the pilot to hold the lever in such position.. Should the aircraft now fly higher than the critical altitude for the selected engine speed, the differential lever 14, 28 will be moved automatically until an arm 28a, Fig. 6, thereon engages the shaft 20, whereupon the lever pivots about the shaft 20 instead of the stud 17a and turns the shaft 20 back slightly, reducing the - inlet manifold pressure to a pressure safe for the actual speed of the engine. To permit this action, the resilient connection between the arms 186A and 186B of the control lever 186. yields.